The invention relates to a power generator unit composed of a generator and a piston internal combustion engine as the drive, particularly composed of a synchronous generator and a diesel engine, with permanent magnets arranged in the rotor of the generator, in the area of the poles, for its excitation, and a rotor winding in the stator.
Such a power generator unit, combined with a pump unit, is described in DE 19721527.
Permanently excited electrical machines usually possess permanent magnets that consist of one piece per pole. In the known generator, each permanent magnet possess the shape of a cylinder mantle segment, which borders the air gap formed with the stator, in the region of the poles.
Such permanent magnet shells are not easy to produce in economically efficient manner, at least not in a size that is suitable for generators with an output of more than five kVA. The installation of such one-piece permanent magnets is only possible in the non-magnetized state, because of the great magnetic forces that preclude any normal handling. Magnetization must then be performed on the completely assembled rotor, which is a complicated process. During the transport of such large permanent magnets, there is also the risk of breakage, because of their brittle material properties.
In contrast, the present invention is based on the task of creating an economically efficient solution for fitting the rotor of the generator, in the power generator unit mentioned initially, for the purpose of magnetic excitation of the generator and, in particular, of avoiding the aforementioned disadvantages.
This task is accomplished, with regard to the production of the permanent magnets as well as with regard to their installation in the rotor of a power generator unit as stated initially, in accordance with the characteristic of claim 1.
Because the permanent magnets are formed by a plurality of relatively small magnet elements, according to a proposal of the invention, on the one hand, it becomes possible to produce them in economically efficient manner. Such elements are not only easy to transport and easy to produce in the magnetized state, but can also be installed in simple manner. For this purpose, they are individually arranged in suitable holder pockets of the rotor, next to one another in the circumference direction, with their poles aligned the same way. These pockets are structured to be open on one or both sides, viewed in the axial direction, so that it is possible to fit the magnet elements into them from one or both faces of the rotor. Holder pockets structured to be continuous in the axial direction and open make it possible, as an advantageous embodiment, for the magnet elements to be arranged in at least two rows, in the axial direction, in the holder pockets. In this connection, there is the possibility of adapting the magnetic flow to be achieved to any desired design, by way of the magnet elements, by choosing their size and shape, number, and arrangement accordingly. For this purpose, the magnet elements can be arranged more or less close to one another; they can be arranged in one or in two or even in several rows, in the axial direction. In connection with their size, the radial thickness, which significantly determines the density of the magnetic flow, must be taken into particular consideration. In contrast, the length and the width of the magnet elements are non-critical for the magnetic resistance. Instead, the latter is dependent not only on the radial dimension of the magnet elements, but also even more on their number, i.e. on the arc length of the holder pockets fitted with magnet elements. In addition, the level of the exciter voltage can also be easily changed in that a small number of magnet elements with the same size and shape is moved, so that more or less large gaps between adjacent magnet elements are formed. These can be filled with replacement pieces made of plastic, if necessary, which take on the role of filling the space.
As far as the shape of the magnet elements is concerned, it can be practical to determine their length in accordance with the axial dimension of the rotor, e.g. in that the axial width of the rotor corresponds to a multiple, e.g. about twice the length of a magnet element.
With regard to their cross-section structure, the magnet elements can be structured as ring segments or rectangular, for example. In the latter case, it is advantageous if the radial inside surfaces of the holder pockets are structured in polygon shape, adapted to the segments, so that the block-shaped magnet elements rest against the polygon surfaces with their large surfaces, in each instance.
To improve the installation of the magnet elements, an advantageous further development consists of the fact that at least on the inside surface of the holder pockets that lies opposite the circumference wall, ribs are provided that run axially and define the distances between adjacent magnet elements.
The magnet elements are held in place in their installation position, in each instance, as a result of the great magnetic forces. However, it can also be practical to attach the magnet elements on the inside surface of the holder pockets by gluing them in place, in addition, or to cover the holder pockets with corresponding lids made of metal or plastic at their faces that lie axially opposite.
Also to simplify the installation, or for considerations of statics, it can be practical to divide the holder pockets into individual drawers that each correspond to approximately the cross-section of a magnet element, by means of partitions that run axially.
The magnet elements are arranged in the rotor of the generator. In this connection, the rotor can be structured as an external rotor, according to the invention. Vice versa, however, the rotor with the magnet elements can also be structured as an internal rotor, where the rotor winding is then located in the stator, which is arranged on the outside.
In order to prevent the edge-side magnet elements from becoming unusable as a result of magnetic reversal in the case of a so-called surge short-circuit, a deflection of the magnetic flow is provided, according to the invention, in such a way that the holder pockets are extended in the circumference direction, on both sides, going beyond the magnet element, in each instance. This prevents the permanent magnets from being demagnetized.
With the holder pockets for the magnet elements provided according to the invention, there is the possibility of simple installation of the magnet elements, which can be positioned almost without any force, as a result of the magnetic ground. In addition, it can be practical to use a magnetic field influence during installation; for this purpose, it can be provided, according to another proposal according to the invention, that a stator is positioned inside the rotor during installation, to which current is applied during the installation, in such a way that positioning of the magnet elements can take place essentially without any force. In this way, installation difficulties resulting from strong repulsion forces between the magnet elements are avoided. With this interaction of the structure of the holder pockets, on the one hand, and fitting them with permanent magnets in the form of small magnet elements, on the other hand, an economically efficient way was found to implement such power generator units with a permanently excited synchronous generator.